The lift of a wing, in part, is proportional to its coefficient of lift, its area, and the square of its velocity as it moves through the air. Thus, at cruising speed, the wing area and the coefficient of lift required to maintain the aircraft's altitude is considerably less than that required at takeoff or for slow approach landing speeds. Sizing the wing for these latter conditions, which exist for only a relatively brief period during a flight, would result in gross inefficiencies during the rest of the flight regime. In such a case, the aircraft would carry the excess weight of the larger wing throughout the flight and would be subjected to a large drag penalty because of the greater wing surface area. The end results would be a reduced payload and higher fuel consumption.
This problem has been solved in the past by incorporating into the wing devices such as leading and trailing edge flaps which can be extended as required, thereby effectively increasing both the wing area and the coefficient of lift by increasing the mean camber line of the wing.
The introduction of new aircraft having wings with sharp leading edges, a significant amount of space behind the leading edge being reserved for incorporation of special material, and the need for leading edge boundary layer control have made the designing of wings more difficult. Prior art systems basically have not been able to meet these additional design requirements.
For example, prior art systems such as disclosed in U.S. Pat. No. 3,556,439, "Method and High Lift Systems for Making an Aircraft Wing more Efficient for Takeoff and Landings," by Charles P. Autrey, et al, provide a large increase in wing area and camber by extending and drooping the front portion of the wing and further extending a three-segment leading edge flap downwardly and forwardly of the leading edge. While having the advantages noted above, such designs have the disadvantage of being extremely complicated and the actuator system occupies the leading edge portion of the wing.
In order to reduce the volume occupied by a multisegment leading edge flap, past designs have attempted to make use of a portion of the bottom surface of the wing as a flap segment. For example, U.S. Pat. No. 3,504,870, "Aircraft Wing Variable Camber Leading Edge Flap," by J. B. Cole, et al, uses a relatively flat portion of the bottom surface of the wing which extends forwardly and downwardly from the leading edge. The flat portion is then warped into an aerodynamic surface by a sophisticated linkage system. While this design reduces the volume occupied by the leading edge flap, it still requires a complex actuation mechanism which intrudes into the leading edge portion of the wing.
It is also a desirable feature to have some form of boundary layer control typically provided by ejecting air over the top surface of the wing. This assures that at any given speed the boundary layer does not separate until a much higher angle of attack and higher coefficient of lift are reached.
U.S. Pat. No. 3,831,886, "Airfoil with Extrudable and Retractable Leading Edge" by Burgess, et al, design provides for boundary layer control. But the very fact that the leading edge is translated forward requires a flexible connection between the leading edge and the air supply ducts. This has disadvantages in that such flexible connections are subject to fatigue failure.
Other patents of interest are U.S. Pat. No. 4,285,482, "Wing Leading Edge High Lift Device," by D. S. Lewis, U.S. Pat. No. 4,099,691, "Boundary Layer Control System for Aircraft," by E. W. Swanson, et al, and U.S. Pat. No. 4,398,688, "Leading Edge Flap for an Airfoil," by A. L. William, all of which incorporate actuating mechanisms in the leading edge portion of the wing.
From the foregoing, it can be seen that it is a primary object of this invention to provide a leading edge flap for a wing having a sharp leading edge that can be stored within the wing in a minimal space when retracted. This is accomplished while still providing, when the flap is extended, an increase in wing area and camber, as well as a larger effective leading edge radius.
It is another object of this invention to provide a leading edge flap that can be stored a significant distance from the leading edge of the wing.
It is also an object of this invention to provide a leading edge flap having a simplified actuation system, with all hinge brackets and actuators being located inside the wing contour.
A still further object of this invention is to provide a leading edge flap system having provisions for boundary layer control.